Respect the NO_COLOR environment variable

See <https://no-color.org/>

Support for CLICOLOR and CLICOLOR_FORCE is a bigger change,
and will have to wait till v2.10.
See <https://bixense.com/clicolors/> for more details.

Author: Techcable

CHANGELOG.md

@@ -15,6 +15,11 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 [slog#267]: https://github.com/slog-rs/slog/issues/267
 
+### Changed
+* Respect the [`NO_COLOR`] environment variable.
+
+[`NO_COLOR`]: https://no-color.org/
+
 ## 2.9.1 - 2024-02-18
 ### Fixed
 * Switch from `atty` to `is_terminal`

src/lib.rs

@@ -1404,6 +1404,10 @@ enum AnyTerminal {
 
 impl AnyTerminal {
     fn should_use_color(&self) -> bool {
+        // Respect NO_COLOR <https://no-color.org/>
+        if std::env::var_os("NO_COLOR").map_or(false, |x| !x.is_empty()) {
+            return false;
+        }
         match *self {
             AnyTerminal::Stdout { .. } => std::io::stdout().is_terminal(),
             AnyTerminal::Stderr { .. } => std::io::stderr().is_terminal(),